It is known in the art to provide vacuum pumps for use with automotive vehicle engines and the like. Such pumps may be provided with a reciprocable pumping member actuated by a cam driven by a drive gear, all supported in a housing. The housing may be mountable in the engine block for engagement of the drive gear with a camshaft gear or other gear for driving the pump. Such an arrangement is shown, for example, in U.S. Pat. No. 4,156,416, granted May 29, 1979 and assigned to the assignee of the present invention. In this prior arrangement the drive gear drives an eccentric, or single lobed cam, that actuates the push rod of the pumping element, which is biased against the eccentric by a return spring.
While the foregoing construction is providing very satisfactory operation in commercial use, it was desired to provide an additional pump model with substantially increased pumping capacity at the same operating speeds. This was accomplished by substituting a three-lobed cam for the single eccentric of the previous embodiment, thus tripling its pumping rate. However, tests revealed that this change caused a significant problem of drive gear chatter, resulting in problems of excessive noise and gear wear during pump operation.